Expandable stent apparatus and method

ABSTRACT

An expandable stent has a sheeted material which is expanded from a compacted configuration to an expanded configuration. The sheet is maintained in the compacted configuration at least in part by operation of a dynamic force, and the expansion occurs at least in part by removal of the dynamic force. In preferred embodiments, a biocompatible sheeted material is wrapped around a split reed grasper to produce a compacted configuration, and the split reed grasper is rotated to maintain the compacted configuration during insertion of the stent into a patient. The rotation is continued while the stent is positioned, and then the rotation is stopped or slowed to permit expansion of the sheet.

RELATED PATENTS

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/780,883 filed Feb. 9, 2001, now U.S. Pat. No. 6,406,487,which is a continuation of U.S. patent application Ser No. 09/372,711,filed Aug, 11, 1999, now U.S. Pat. No. 6,187,015, which is acontinuation of U.S. patent application Ser. No. 08/850,320 filed May 2,1997, now U.S. Pat. No. 5,957,929.

FIELD OF THE INVENTION

[0002] This invention relates to expandable stents.

BACKGROUND OF THE INVENTION

[0003] Stents are endoprostheses which can be deployed into the lumen ofan artery or vein, a common bile duct, the urethra or other bodypassageway. Stents may be employed in such passageways for manypurposes, including expansion of a lumen, maintenance of the lumen afterexpansion, and repair of a damaged intima or wall surrounding a lumen.With respect to arteries, for example, stents may be used as, or inconjunction with, intralumenal grafts in the maintenance of patency of alumen following angioplasty. In such cases a stent may be used toprevent restenosis of the dilated vessel, to prevent elastic recoil ofthe vessel, or to eliminate the danger of occlusion caused by “flaps”resulting from intimal tears associated with the angioplasty. In otherinstances, stents may be used to treat aneurysm, tears, dissections andother continuity faults, as, for example, in the splenic, carotid, iliacand popliteal vessels. By way of further example, it is known to use astent to maintain the patency of a urethra compressed by an enlargedprostate gland.

[0004] In one class of expandable stents commonly referred to as“rolled” stents, a sheeted material is rolled onto the outer distalcircumference of a support member or “core”. The sheeted material isthen positioned at a targeted treatment area and expanded. Rolled stentscan be characterized according to: (1) the method by which the rolledsheet is maintained in a compressed configuration; and (2) the method bywhich the sheet is expanded.

[0005] Lane, Self Expanding Vascular Endoprosthesis for Aneurysms, U.S.Pat. No. 5,405,379 (Apr. 11, 1995) describes a stent which employs aself expanding sheet. The sheet is forcibly rolled into a compressedconfiguration, and then inserted into a catheter to maintain thecompressed configuration. Expansion takes place by ejecting the sheetfrom the end of the catheter.

[0006] Kreamer, Intraluminal Graft, U.S. Pat. No. 4,740,207 (Apr. 26,1988) describes a rolled stent in which a sheet of stainless steel isrolled around an angioplasty type balloon. After being introduced into atreatment area, the sheet is expanded by inflating the balloon with afluid. In this case compression is maintained during the early stages ofdeployment by the relaxed nature of the sheet in the compressedconfiguration, i.e., the internal mechanical resistance of the sheet todeformation. Expansion of the sheet, on the other hand, occurs underradial pressure exerted by the expanding balloon.

[0007] Sigwart, Intravascular Stent, U.S. Pat. No. 5,443,500 (Aug. 22,1995) describes a stent in which a flat sheet is perforated to form areticulated or lattice type structure having a ratcheting lockingmechanism. Compression in stents according to the Sigwart patent aremaintained by a holding wire or adhesive, and the sheet is contemplatedto be expanded under the influence of an angioplasty balloon.

[0008] Sigwart also describes another stent comprising an elasticstainless steel mesh. The diameter of the mesh is slightly larger thanthe normal inner diameter of the vessel to be treated, so that the meshcan exert a residual radial pressure on the arterial wall after beingimplanted. Before being introduced into a patient's blood vessel thestent is reduced in diameter. The reduced diameter is maintained whileadvancing the stent into a target treatment area by an outer sleeve.Once the device is implanted, the stent is deployed by withdrawal of theouter sleeve. In this instance, compression is thus maintained by theouter sleeve, and expansion is achieved by removal of the outer sleeve.

[0009] Alfidi and Cross, Vessel Implantable Appliance and Method ofImplanting It, U.S. Pat. No. 3,868,956 (Mar. 4, 1975) describes a stentwhich utilizes a recovery alloy such as nitinol. In such stents aninitial expanded configuration is permanently set into the alloy byheating the material to a relatively high temperature while the alloy ismaintained in the expanded configuration. The alloy is then cooled anddeformed to a compressed configuration. The compressed configuration isretained at room temperature, but recovers to the expanded configurationwhen reheated to a transition temperature. Here, compression ismaintained during the early stages of deployment by the internalmechanical resistance of the alloy against deformation, and the sheet isexpanded under the influence of heat.

[0010] These and all other known teachings reflect the accepted wisdomthat rolled stents are to be maintained in their compressedconfigurations by the operation of static forces (e.g., biasing producedby the internal mechanical resistance of the sheet to deformation,presence of holding wires, outer sleeves and so forth), while expansionof the sheeted materials is to be produced by application of a dynamicforce (e.g., radial pressure exerted by an expanding balloon,application of heat, removal of a holding wire or sheath, and so forth).While such strategies undoubtedly have their benefits, it is useful tohave stents which operate outside of these accepted constraints.

[0011] Where the stent is to be deployed in very small vessels of thebody, such as the arteries in the brain, the size of the stents is quitesmall, and the material used for the stents is on the order of0.0001-0.0004 inches thick. The small size and extreme thinness of thestent material makes it difficult to deploy the stent using the typicalpush-pull type deployment mechanisms generally used for stents. Thefrictional force exerted on the stent by the catheter sheaths and coresas they slide over the stent often tears the stent. In our co-pendingU.S. patent application Ser. No. 08/762,110, filed Dec. 9, 1996, weprovide a number of devices that do not require any sliding movement ofthe stent or catheter sheath relative to each other. The devicesdescribed below provide additional mechanisms and methods for deployingstents while minimizing the frictional forces operating between thestents and the catheters used for their insertion.

SUMMARY OF THE INVENTION

[0012] Stents for intra-cranial use and methods for using these stentsare described in detail below. The physical characteristics of prior artballoon expandable stents and self expanding stents make them clearlyunsuitable for intra-cranial use, because of their delivery profile,their lack of flexibility and their tendency to temporarily occlude thevessel during deployment. They have not been proposed for intra-cranialuse. Palmaz stents, Palmaz-Schatz™ stents, Wallstents, Cragg stents,Strecker stents and Gianturco stents and other stents are too rigid toallow placement in the cerebral blood vessels, some require a balloonfor deployment, and all are too open to occlude or prevent blood flowinto an aneurysm. Presented below are several embodiments of stentssuitable for intra-cranial use, along with methods for using thesestents to treat intra-cranial vascular disease.

[0013] The self expanding rolled sheet stent is suitable for use in theintra-cranial arteries. The rolled sheet is made of Elgiloy™, nitinol,stainless steel, plastic or other suitable material, and is impartedwith resilience to urge outward expansion of the roll to bring therolled stent into contact with the inner wall of a diseased artery. Therolled sheet is adapted for easy insertion and non-deforming radialflexibility to facilitate tracking along the tortuous insertion pathwaysinto the brain. In some embodiments, as much of the material of thestent is removed as is consistent with eventual creation of a solidwalled stent upon unrolling of the stent within the blood vessel. Theunrolled stent may be two or more layers of Elgiloy™, thus providingradial strength for the stent and creating at least a slight compliancemismatch between the stent and the blood vessel, thereby creating a sealbetween the stent and the blood vessel wall. For placement, the stent istightly rolled upon or captured within the distal tip of an insertioncatheter. The release mechanism is extremely low profile (3 Fr or less),and permits holding the rolled stent in a tight roll during insertionand permits atraumatic release when in the proximity of the site ofarterial disease, without completely occluding the vessel with thedeployment catheter. The stent can be placed in the intra-cranial bloodvessels (arteries and veins) of a patient to accomplish immediate andcomplete isolation of an aneurysm and side branches from the circulatorysystem. The stent can be placed so as to partially occlude or modifyblood flow into an aneurysm. The stent can be placed so as to allow forinjection of coils (GDC coils or Gianturco coils) or embolic materialinto an aneurysm and prevent wash-out of the coils or embolic material.The stent may be placed across a target site such as an aneurysm neck,origin of a fistula, or branch blood vessels feeding a tumor in order toredirect the flow of blood away from the target. It can be used as astand alone device which is left in the intra-cranial arterypermanently, or it may be used as a temporary device which allows forimmediate stabilization of a patient undergoing rupture of a bloodvessel an aneurysm or awaiting open skull surgery for clipping orresection of an aneurysm. The stent can be used for stabilization andisolation of a vascular defect during surgery of the vascular defect.Another advantage of this type of stent is that it can be wound downshould repositioning be required prior to full release. It is possibleto rewind and reposition or remove the device using a crooked rotatingwire or other grasping tools.

[0014] The present invention is directed to expandable stents having asheeted material configurable in both a compacted configuration and anexpanded configuration, in which the compacted configuration duringdeployment is maintained at least in part by operation of a dynamicforce, and expansion to the expanded configuration occurs at least inpart by removal of the dynamic force.

[0015] In preferred embodiments, a biocompatible sheeted material iswrapped around a retaining wire to produce the compacted configuration,and the retaining wire is rotated to maintain the compactedconfiguration during insertion of the stent into a patient. The rotationis continued while the stent positioned, and then the rotation isstopped or slowed to permit expansion of the sheet. Counter rotation maybe used to enhance expansion, if desired.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a schematic diagram of the vasculature of the brainshowing a typical placement of an intra-cranial stent.

[0017]FIG. 2 is schematic diagram of the vascular of the brainillustrating the circle of Willis and arteries supplying the circle ofWillis.

[0018]FIG. 3 is a diagrammatic representation of a stent according tothe present invention.

[0019]FIG. 4 is a diagrammatic representation of a motor drive used forthe stent and its connection to the system.

[0020]FIG. 5a, 5 b and 5 c are a diagrammatic representations of a thestent in the process of deployment.

[0021]FIGS. 6A, 6B, 6C, 6D and 6E illustrate various methods ofattaching and detaching a stent from the insertion catheter.

[0022]FIG. 7 shows an embodiment of the rotating stent deployment systemwith a tear-away tab release.

DETAILED DESCRIPTION OF THE INVENTIONS

[0023] The stent delivery system is particularly well suited fordelivery of stents into very small vessels in the body, such as theblood vessels within the brain. FIGS. 1 and 2 show the vasculature ofthe brain in sufficient detail to understand the invention. The brain 3is supplied with blood through the carotid and the vertebral arteries oneach side of the neck. The important arteries include the common carotidartery 4 in the neck, which will be the most common access pathway forthe stent, the internal carotid 5 which supplies the opthalmic artery 6.The external carotid 7 supplies the maxillary artery 8, the middlemeningeal artery 9, and the superficial temporal arteries 10 (frontal)and 11 (parietal). The vertebral artery 12 supplies the basilar artery13 and the cerebral arteries including the posterior cerebral artery 14and the circle of Willis indicated generally at 15. Also supplied by theinternal carotid artery are the anterior cerebral artery 16 and themiddle cerebral artery 17, as well as the circle of Willis, includingthe posterior communicating artery 18 and the anterior communicatingartery 19. These arteries typically have an internal diameter of about 1mm to 5 mm, most commonly from 2-4 mm. The methods and devices describedherein allow access to these arteries and placement of a stent in thesearteries. In FIG. 1, the insertion catheter 2 and stent 1 are shown inan exemplary use, threaded through the common carotid artery 4 and theinternal carotid artery 5, with the stent extending into the anteriorcerebral artery 16. The rotating wire 20 extends from the proximal endof the insertion catheter 2 to the distal end, and into the stent toimpart rotation to the stent.

[0024]FIG. 2 shows the same blood vessels in a schematic view thatbetter illustrates the circle of Willis and the arteries which supplythis important anatomic feature. The circle of Willis 15 is a ring ofarteries connecting the internal carotid arteries and the basilar artery(and hence the left and right vertebral arteries) to the anteriorcerebral arteries 16, middle cerebral arteries 17 and posterior cerebralarteries 14. The system provides a redundant supply of blood to thecerebral arteries. Aneurysms, fistulas, AVM's and tumors occurringinside the brain, in the intracranial portion of the carotid arteries,vertebral arteries and basilar artery, in the circle of Willis or evendeeper within the brain may be treated with the stents and deliverysystems described below. FIG. 2 shows an exemplary use in which adelivery catheter 2 is inserted through the aorta into the commoncarotid, internal carotid and through the circle of Willis 15 into themiddle cerebral artery 17 to treat an aneurysm 21 with a stent which isdeployed while being rotated by rotating wire 20, as explained below.

[0025] In FIG. 3, the structure of the stent and stent delivery systemare shown in detail. The stent 10 used with the system generallycomprises a rolled sheet 22. The rolled sheet is sized appropriately toboth fit within a delivery sheath when rolled tightly, and fit snuglywithin a blood vessel when released and allowed to open to a looselyrolled configuration. The sheet 22 is releasably coupled to theinsertion catheter 2 via the retaining wire 20 which has a tightly bentcrook 23 which grasps the inner edge 24 or the stent. The retaining wire20 is rotated in the direction of arrow 25 such that the sheet 22 tendsto wrap around the retaining wire 20. Rotation in this manner tends tocause the sheet 22 to assume an at least partially compactedconfiguration. The sheet is 22 initially wrapped around the retainingwire and slipped into the distal end 26 of the insertion catheter. Oncecompacted in this manner, the stent 10 can be introduced into theinsertion catheter 2 for deployment into an artery or other passageway.When inserted into the insertion catheter 2, the retaining wire securelyholds the stent in the tight roll within the insertion catheter.

[0026] The proximal end of the stent delivery system is shown in FIG. 4.The retaining wire 20 is attached at its proximal end 30 to a proximalhub 31 and an electric motor 32 which is housed within the handle 33.The motor 32 is used to rotate the retaining wire 20 and the stent 1.The motor may be operated to rotate the retaining wire 20 and the stent1 in the direction which urges sheet to tighten upon itself and remainin a small diameter configuration (indicated by arrow 25). The motor iscontrolled with a spring loaded thumb slide 34. A portion of the stent 1passes through a catheter 2, but during at least a portion of its travelduring deployment in a target lumen, the sheet is maintained in acompacted configuration at least partially as a result of continuedrotation of the stent 1 by the motor 32.

[0027] The motor 32 is presently contemplated to have an operationalrange of between zero and 200 revolutions per minute (rpm). It isconsidered advantageous for the motor 32 to include a variable speedcontrol, and the motor may have a reverse mode. The motor may be batteryoperated to avoid the need for a power cord. It is also desirable tohave a manual turning device, such as the proximal hub 31 which isconnected directly to the retaining wire 20, or to the motor 32, orindirectly coupled to the retaining wire 20 through a clutch mechanism.For small rotations needed for some manipulations of the stent duringand after placement, it is sufficient to rotate the entire handle andmotor assembly by hand. A typical retaining wire comprises a wire100-175 cm long, and may measure about 0.005 to 0.020 inches (5-20 mils,or 0.1-0.4 mm) in diameter. Of that length, about 0.5 cm at the distalend is bent around to form the retaining wire crook. The proximal end isattached to the proximal hub connector in motor and handle assembly. Theretaining wire may be releasably attached with connections such as thecouplings typically used for rotational atherectomy catheters andintravascular ultrasound catheters. Preferred materials for theretaining wire include stainless steel and nitinol.

[0028] Turning in greater detail to specific elements of the stent 1, itshould be apparent that the sheet 22 can have any suitable composition,surface characteristics, shape, thickness, elasticity and so forth. Whenused in the illustrated use for blocking off side wall aneurysms or sidevessels in an artery, the stent sheet material is preferably made ofElgiloy or nitinol (with nickel-rich nitinol being preferred). Thesheets preferably comprise biocompatible material, but there may becircumstances in which stent is to be used for occlusion or tissuedisruption, in which case a non- or only minimally compatible materialmay be preferred. Biocompatible materials include various metals,synthetics and ceramics, and may also include living tissue or acomposite of living tissues and non-living material such as described inTuri, Composite Intraluminal Graft, U.S. Pat. No. 5,556,414 (Sep. 17,1996). Thus, the terms “sheet” and “sheeted material” are used herein ina very broad sense, including relatively thin meshes and other materialshaving a relatively large flattened surface.

[0029] Sheets according to the present invention may advantageously havea smooth outer surface to minimize trauma to tissues with which thesheet comes in contact. The surface may also include an anti-restenosiscoating such as heparin, fibrin or a fibrin/elastic compound. Otheruseful coatings, such as a degradable mucin or other coating to minimizefriction, may also be used. The stent may be treated so as to beradioactive, in order to minimize hyperplasia and excessive neointimalgrowth. A radiographically opaque coatings, such as tin or platinum,have proven to enhance radiographic visibility of the stent during andafter deployment. Tantalum plating of about 1000 to 10,000 Å thicknessis sufficient to provide good visibility of the stent when rolled inmany layers within the insertion catheter, and a plating of 500 to 5000Å on both sides of the sheet is sufficient for good visibility of thestent when expanded into just a few layers within the blood vessel.

[0030] As with the other characteristics mentioned herein, there arenumerous contemplated variations for the shape and thickness of thesheet. The sheet should have sufficient size and stiffness to handle therelatively high stresses involved. Thus, the length of the sheetemployed to treat aneurysms of the carotid arteries in an adult male mayadvantageously measure about 2.5 mm in longitudinal length 1 and about40 mm in wrap length w. For aneurysms of the cavernous carotid arteries,the stent may be telescoped to cover distances as much as 10 mm or more.Where the stent is deployed in smaller vessels, however, such as thecerebral arteries, the corresponding dimensions may be 1 mm in lengthand 20 mm in wrap length. The thickness may measure 0.0001′ to 0.0004′(0.1-0.4 mil, or 0.0025-0.01 mm) when the sheet is made of Elgiloy. Thethickness of 0.0002-0.0003″″ (0.2-0.3 mil, or 0.0050-0.0075 mm) hasworked best in bench tests and animal studies, resulting in negligiblecrimping from the crook and providing for easy deployment without thetearing associated with push-type deployment methods. Nitinol sheets maybe slightly thicker and may allow for greater radial force applied bythe stent against the blood vessel wall. The wrap length of the stentmay vary according to the size of the target vessel and the number ofoverlapping layers desired in the deployed configuration.

[0031] The stent sheets may be perforated to any degree necessary toencourage tissue ingrowth or to allow for some blood flow through thestent wall. Although the sheets illustrated are rectangular or ribbonshaped, the sheets used for the stents need not be rectangular. Atriangular shape, for example, may also be feasible, with either an edgeor a point of the triangle being grasped by the retaining wire. The wraplength of the sheet may be variable, and may be long enough to wrap thesheet around itself three, four, five or more times, or it may be shortenough so that the wrap length is substantially equal to thecircumference of the target vessel, in which case the sheet will have asingle layer after deployment. In such cases, it may be desirable totranslate the retaining wire within the lumen back and forth duringdeployment to reduce the possibility of gaps. The stent may betelescoped to allow for greater length than its straight rolledconfiguration would otherwise allow. Also, the rotational method ofdeployment may be used with the extreme cases of a wire coil stentwherein the stent comprised a coil of round or square wire (as opposedto the ribbon shape used in the illustrations).

[0032] The use of Elgiloy™ or nitinol provides elasticity that issuitable for easy deployment of the stent, providing for adequate selfexpandability and also providing adequate strength for the stent afterdeployment. The crimping at the inner edge of the stent, where the crookgrasps the sheet, is negligible or acceptably small with Elgiloy andnitinol. Other materials may be used which provide relatively more orless of a self expanding quality. One alternative is to make the sheetwith material that has high elasticity, and will expand to asubstantially predetermined shape upon cessation of rotation. In otherinstances, the sheet may have little or no elasticity, and may beoptimally deployed by ceasing rotation, and then unwinding the sheet byrotation in the opposite direction, by balloon expansion, or otherwiseapplying active force upon the sheet. There may also be greaterelasticity in one dimension than in another

[0033] Lumenal deployment occurs by rotating the stent 1 while extendingit from the open distal end of the catheter. While still under theinfluence of continued rotation, the stent 10 is pushed from the distalend of the insertion catheter, using the motor and handle assembly. Thestent is navigated through any length of blood vessel while rotating,and fed to a target area for deployment, where the rotation is stoppedor even reversed slightly to unwrap the sheet 22. Simple manual rotationof the retaining wire may be used to assist in proper deployment. Thestent 1 is then pushed, pulled, or otherwise manipulated to free theretaining wire 20 from the sheet, and the stent is withdrawn. FIGS. 5a,5 b and 5 c illustrate the method of deployment of a stent which isenabled by the device. In FIG. 5a the stent 1 is positioned at thedistal end of the insertion catheter 2. The stent is still wrappedaround the retaining wire and secured by the crook of the wire. In FIG.5b, the retaining wire 20 is rotated in the direction necessary totighten the stent, and this rotation causes the stent to tighten into atighter roll (the diameter may remain the same or become smaller,depending on the speed of rotation and the flexibility of the stent) andalso causes the stent to rotate with the retaining wire. As illustratedin FIG. 5b the stent 1 is advanced out insertion catheter 2. Thelongitudinal movement of the stent within the insertion catheter isfacilitated by the rotation, and the stent 1 is maintained in atightened configuration by rotation of the retaining wire 20 in thedirection of arrow 25. The stent also does not spread longitudinallyduring the rotation, and this also facilitates deployment (although therolled sheet may be telescoped to spread it out and cover a length ofthe blood vessel). Finally, as shown 5 c, the stent is pushedlongitudinally out of the distal end of the insertion catheter and intothe lumen of the blood vessel 35 in position to close off the aneurysm36. The retaining wire may be used to push or pull the stent into betterposition as it is rotating. Rotation is ceased when the position isacceptable, whereupon the stent opens fully. Fully unwinding of thestent can be ensured by counter-rotating the retaining wire (with themotor in reverse, or by hand turning the handle or the proximal hub). Torelease the stent, the retaining wire is pushed distally until the crookslips off the stent. The retaining wire may again be used to push orpull the stent into better position, or adjust the inner layer tocompact or spread the stent longitudinally. The crook may be used tore-engage the stent and resume rotation (in order to move or remove thestent) by advancing the retaining wire to a position distal of the stentand carefully slipping the crook between the layers and resumingrotation. With this technique, the stent may be used as a permanentstent or as a temporary stent, for blood vessels deep within the body,and in particular for blood vessels within the brain. When used as apermanent stent to occlude and aneurysm, the stent may constitute theprimary treatment for the aneurysm. When used as a temporary stent, thestent may be placed to occlude an aneurysm before invasive surgery suchas aneurysm clipping or ligation, thereby eliminating much of the riskinherent in open surgical techniques for treating aneurysms within thebrain. After a successful clipping or ligation, the stent can bere-engaged and rotated, and pulled into the distal end of the insertioncatheter. It should be apparent that, when used as a temporary stent inan interoperative setting, the retaining wire may be left in place andneed not be removed from the stent at any time. The stent may also beused to control blood flow through the neck of an aneurysm inconjunction with coils, embolic materials or other devices, or it mayoperate as a primary treatment.

[0034] Other embodiments of distal rotatable and releasable connectionmay be used. As discussed above, the rotation of the stent isaccomplished with the crooked retaining wire 20. Other stent rotationmeans are shown in FIGS. 6A through 6E. In FIG. 6A, the retaining meanscomprises a rotating shaft 37 with a split reed grasper 38 disposed onthe distal end of the rotating shaft. The inside edge of the stent istrapped in the split reed, so that when the rotating shaft is spun fromthe distal end the stent is spun at the distal end. The stent isreleased when the split reed is pulled into the insertion catheter. FIG.6B includes a compression ring 39 and pullwire 40 (which extends to theproximal end of the catheter) which can be used to compress the splitreed during insertion and rotation, after which the compression ring canbe pull proximally to allow the split reed to open slightly and releasethe stent. In FIG. 6C, the retaining means comprises a hollow shaft 41(such as a hollow guidewire) combined with a pullwire retainer 42 runsgenerally through the center of the hollow shaft and but exits thecenter of the shaft though proximal wire port 43 p, then runs over theinner edge of the stent before reentering the hollow shaft throughdistal wire port 43 d. The stent is thereby trapped by the pullwireretainer 42. Rotation of the hollow shaft 41 causes rotation of thestent to tighten the stent configuration during insertion andlongitudinal movement. When the stent is properly positioned, rotationis stopped and the pullwire retainer is pulled proximally to release thestent. FIG. 6D shows the crooked retaining wire 20, and the stent 1which is trapped in the crook 23. The inner edge 24 of the stent isfolded back, toward the outside surface, to form a flap 44. Thisoutwardly facing flap provides extra holding power for the crook duringrotation of the stent. FIG. 6E discloses yet another embodiment in whichthe stent 1 is retained between two spinning wires, a mounting spinningwire 45 and a retaining pullwire 46. Both wires extend to the proximalend of the insertion catheter 2 where they are attached to the proximalhub and motor. At the distal end, the mounting spinning wire is fixed tothe guidewire tip 47, and the retaining pullwire is not fixed andtherefore can be moved longitudinally in relation to the mountingspinning wire. The space between the wires is maintained tight by therings 48 d and 48 p which are fixed to the mounting spinning wire, andthrough which the retaining pullwire 46 may move longitudinally. Thestent will rotate with the wires, and release may be accomplished bypulling retaining pullwire 46 proximally away from the stent. The stentmay be crimped, folded or provided with a beaded edge 49 on the insideedge 24 to ensure a good grip on the stent. Each of the embodiments canincorporate an integral guidewire tip which extends distally from thecrooked retaining wire or the rotating hollow shaft, as the case may be.Alternatively, the device may be inserted in over the guidewire fashion,or in rapid exchange fashion (in which case the insertion catheter maybe provided with a monorail tip).

[0035] In FIG. 7 another embodiment of the rotating and retaining meansis illustrated. The retaining means comprises a core 50 which includes aretaining wire 51 which is bonded at or near the inner edge 24 of thesheet 22. The starter notch 52 on the stent, located to correspond tothe diameter of the core 43, creates a tear line 53 which separates thesheet into the major portion of the sheet 22 which will remain in theblood vessel after deployment, and a small tear-away tab 54 which willbe torn from the major portion of the sheet in order to release thestent. During deployment the core 43 and the inner wire 44 are rotatedto tighten the stent and facilitate longitudinal movement of the stentout of the distal end of the catheter and within the lumen of the bloodvessel. When the stent is properly placed, the small tear-away tab canbe retracted proximally using several gentle tugs, which strips off themajor portion of the sheet 22 from the inner wire 44. The bonding can beachieved using cyanoacrylate adhesive (super glue) or any other suitableadhesive.

[0036] The various embodiments of the releasable retaining mechanismprovide a dynamic rotational force that maintains the stent in aconfiguration in which longitudinal movement is facilitated. Rotationmay be at such speed as to spin the stent into a smaller diameter, butthis is not strictly necessary. It is sufficient that the stent be urgedtoward a more tightly wound condition, such that the outer layers mayslide more freely over each other and past the inner surfaces of thecatheter and blood vessel. The process is similar to that used to removea roll of paper from a mailing tube, which often requires that the rollbe twisted from an inside layer to loosen the roll within the mailingtube while the roll is pulled from the mailing tube. In this analogoussituation, it is apparent that the roll of paper need not be spun somuch that is actually takes on a smaller diameter, and that it issufficient to remove the outwardly compressive force exerted by theinner rolls as they resiliently try to expand against the outer layers.We say that the roll of paper is rotated to urge the roll toward asmaller diameter configuration, realizing that the smaller diameterconfiguration need never be achieved. We also refer to the configurationachieved by rotation as the compacted configuration, realizing that thisincludes configurations in which inner layers are rotated into a tighterroll but outer layers may be tightened into a smaller diameter or maymerely become loose compared to the inner layers, depending on therotational speed applied. Such a compacted configuration is maintainedat least in part by operation of the dynamic force applied by rotation,and expansion to the expanded configuration occurs at least in part byremoval of the dynamic force.

[0037] Thus, while specific embodiments and applications of expandablestents have been disclosed and described in reference to the environmentin which they were developed, they are merely illustrative of theprinciples of the inventions. Although described in reference to thetreatment of blood vessels, the devices may be employed in any vessel ofthe body. It should be apparent to those skilled in the art that manymore modifications besides those already described are possible withoutdeparting from the inventive concepts herein. For example, it iscontemplated that new and better materials be discovered for use andintravascular stents. Similarly, it is possible to devise a number ofreleasable attachment means in addition to those illustrated. Theinventive subject matter, therefore, is not to be restricted except inthe spirit of the appended claims.

I claim:
 1. A stent and stent delivery system for inserting a stent intoa blood vessel and deploying the stent at a target site within the bloodvessel, said stent delivery system comprising: an insertion catheter ofappropriate diameter, length and flexibility for insertion into theblood vessel and navigation within the blood vessel to a location at ornear the target site; a stent comprising a rolled sheet stent having asmall diameter rolled configuration in which the stent fits within thelumen of the insertion catheter and a large diameter rolledconfiguration in which the stent fits within the blood vessel; a splitreed grasper secured to the rolled sheet stent and extending to theproximal end of the insertion catheter; a means for rotating the splitreed grasper, thereby causing rotation of the rolled sheet stent andfacilitating longitudinal movement of the stent.
 2. The stent deliverysystem of claim 1 wherein the split reed grasper is releasably connectedto the rolled sheet stent.
 3. The stent delivery system of claim 1wherein the means for rotating the movable wire comprises a hand heldmotor.
 4. The stent delivery system of claim 1 wherein the means forrotating the movable wire permits manual rotation of the movable wire.5. The stent delivery system of claim 1 wherein the stent comprises asheet of nitinol.
 6. The stent delivery system of claim 1 wherein thestent comprises a sheet of perforated material.
 7. A stent and stentdelivery system for inserting a stent into a vessel of the body anddeploying the stent at a target site within the vessel, said stentdelivery system comprising: an insertion catheter of appropriatediameter, length and flexibility for insertion into the vessel andnavigation within the vessel to a location at or near the target site; astent having a small diameter configuration in which the stent fitswithin the lumen of the insertion catheter and a large diameter rolledconfiguration in which the stent fits within the vessel; a split reedgrasper secured to the stent and extending to the proximal end of theinsertion catheter; a means for rotating the split reed grasper, therebycausing rotation of the stent and facilitating longitudinal movement ofthe stent.
 8. The stent delivery system of claim 7 wherein the splitreed grasper is releasably connected to the stent.
 9. The stent deliverysystem of claim 7 wherein the means for rotating the split reed graspercomprises a hand held motor.
 10. The stent delivery system of claim 7wherein the means for rotating the split reed grasper permits manualrotation of the split reed grasper.
 11. The stent delivery system ofclaim 7 wherein the stent comprises a sheet of nitinol.
 12. The stentdelivery system of claim 7 wherein stent comprises a sheet of perforatedmaterial.
 13. A stent and stent delivery system for inserting a stentinto a vessel of the body and deploying the stent at a target sitewithin the vessel, said stent delivery system comprising: an insertioncatheter having a lumen; a stent having a small diameter configurationand a large diameter configuration; a split reed grasper attached to ashaft at the distal end of the shaft, said split reed grasper secured tothe stent, wherein rotation of the shaft facilitates moving the stentout of the lumen of the distal end of the insertion catheter; and ameans for rotating the shaft.
 14. The stent delivery system of claim 13wherein the split reed grasper is releasably connected to the stent. 15.The stent delivery system of claim 13 wherein the means for rotating theshaft comprises a hand held motor.
 16. The stent delivery system ofclaim 13 wherein the means for rotating the shaft permits manualrotation of the split reed grasper.
 17. The stent delivery system ofclaim 13 wherein the stent comprises a sheet of nitinol.
 18. The stentdelivery system of claim 13 wherein stent comprises a sheet ofperforated material.
 19. A method of deploying a stent within a vesselin the body, said method comprising: providing an insertion catheterhaving a lumen; rolling a sheet stent onto a split reed grasper, thesheet stent having a compact configuration and an expandedconfiguration; the inside edge of the sheet stent trapped in the splitreed grasper; inserting the stent into the lumen of the insertioncatheter; rotating the split reed grasper and thereby the stent to forcethe stent into the compact configuration; as the split reed grasper andstent are being rotated, moving the stent out of the lumen of thecatheter in the compact configuration; and slowing or ceasing therotation of the stent to permit it to expand to the expandedconfiguration within the vessel.
 20. The method of claim 19, wherein thesplit reed grasper is releasably attached to the stent and the methodfurther comprises the step of releasing the stent from the split reedgrasper.
 21. A method of deploying a stent within a vessel of the body,said method comprising: providing an insertion catheter having a lumen;rolling a sheet stent onto a split reed grasper, the sheet stent havinga compact configuration and an expanded configuration; the inside edgeof the sheet stent trapped in the split reed grasper; inserting thestent into the lumen of the insertion catheter; rotating the split reedgrasper and thereby the stent to force the stent into the compactconfiguration; as the split reed grasper and stent are being rotated,moving the stent out of the lumen of the catheter in the compactconfiguration; slowing or ceasing the rotation of the stent to permit itto expand to the expanded configuration within the vessel; releasing thestent from the split reed grasper; re-engaging the stent with the splitreed grasper and rotating the stent; and moving the stent longitudinallywithin the vessel while rotating the stent in order to retrieve thestent from the vessel and pull it into the insertion catheter.
 22. Amethod of deploying a stent within a vessel in the body, said methodcomprising: providing an insertion catheter having a lumen; rolling asheet stent onto a split reed grasper, the sheet stent having a compactconfiguration and an expanded configuration; the inside edge of thesheet stent trapped in the split reed grasper; inserting the stent intothe lumen of the insertion catheter; operating a motor to rotate thesplit reed grasper, and thereby the stent, to force the stent into thecompact configuration; rotating the motor to rotate split reed grasper;as the split reed grasper and stent are being rotated, moving the stentout of the lumen of the catheter in the compact configuration; andslowing or ceasing the rotation of the stent to permit it to expand tothe expanded configuration within the vessel.
 23. The method of claim22, wherein the split reed grasper is releasably attached to the stentand the method further comprises the step of releasing the stent fromthe split reed grasper.
 24. A method of deploying a stent within avessel of the body, said method comprising: providing an insertioncatheter having a lumen; rolling a sheet-stent onto a split reedgrasper, the sheet stent having a compact configuration and an expandedconfiguration; the inside edge of the sheet stent trapped in the splitreed grasper; inserting the stent into the lumen of the insertioncatheter; operating a motor to rotate the split reed grasper, andthereby the stent, to force the stent into the compact configuration;rotating the motor to rotate split reed grasper; as the split reedgrasper and stent are being rotated, moving the stent out of the lumenof the catheter in the compact configuration; slowing or ceasing therotation of the stent to permit it to expand to the expandedconfiguration within the vessel; releasing the stent from the split reedgrasper; re-engaging the stent with the split reed grasper and rotatingthe stent; and moving the stent longitudinally within the vessel whilerotating the stent in order to retrieve the stent from the vessel andpull it into the insertion catheter.